1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a method for reducing the effects of printhead carrier disturbance during printing with an imaging apparatus.
2. Description of the Related Art
An imaging apparatus may be, for example, a printer or a multifunction unit. Such a printer may be, for example, an ink jet printer having an ink jet print engine. Such a multifunction unit may include an ink jet print engine, and is configured to perform standalone functions, such as copying or facsimile receipt and transmission.
Typically, an imaging apparatus having an ink jet print engine includes a reciprocating printhead carrier that transports one or more ink jet printheads across the print medium along a bi-directional main scanning direction, also commonly referred to as the horizontal direction. Printing may take place during one or more unidirectional scans, i.e., passes, of the printhead carrier, e.g., a left-to-right scan and/or a right-to-left scan.
An image is formed on a print medium by ejecting ink from at least one ink jet printhead to form a pattern of ink dots on the print medium. Typically, each ink jet printhead will include one or more columnar nozzle arrays, each having a plurality of ink jet nozzles for expelling the ink. In ink jet printing, it is common to use the ink colors of cyan, magenta, yellow and black, in full strength and/or diluted forms, in generating color prints.
An indexing mechanism is used to incrementally advance the print medium in a sheet feed direction, also commonly referred to as a sub-scan direction or vertical direction, through a printable region (also sometimes referred to as a print zone) between passes of the printhead carrier in the main scanning direction, or after all data intended to be printed on the print medium has been completed.
One type of printing defect common to ink jet print engines is often referred to as vertical banding. Vertical banding defects in multi-color printing are typically observed as a repeating pattern of vertical light bands and vertical dark bands in a printed image, and may also appear in multi-color form similar to that of a rainbow. Vertical banding may also appear in a more rainbow-like repeating pattern. In either case, the printing defect resembles vertical blinds or bands. Vertical banding defects are particularly noticeable in high density ink jet printer printouts, such as when attempting to produce photographic quality printouts, but also can be observed in lower density printouts as well. It has been recognized that printhead carrier disturbances, in the form of printhead carrier vibration, for example, contribute to vertical banding.
FIG. 1 illustrates the general concept of the printhead carrier disturbance, showing the velocity and carrier disturbance versus carrier position during a printhead carrier movement across the print medium (i.e., in the main scanning or X direction). Waveform 8 depicts printhead carrier velocity, in inches per second (ips). Waveform 9 depicts an exemplary printhead carrier disturbance in terms of generated dot placement error in microns (um) in the sub-scanning direction, i.e., the Y-direction, at a disturbance frequency of 50 hertz (Hz), i.e., with a period of 20 milliseconds (ms). Thus, as the printhead carrier moves across the print medium in the main scanning direction, i.e., the X-direction, the printhead carrier can oscillate, which causes ink dot placement errors in the sheet feed direction, i.e., the Y-direction. This phenomenon is detrimental to print quality, yielding vertical banding and varying grain artifacts.
What is needed in the art is a method for reducing the effects of printhead carrier disturbance during printing with an imaging apparatus.